1. Field of the Invention
The present invention relates to a built-in antenna of a portable terminal. More particularly, the present invention relates to a re-configurable built-in antenna of a portable terminal implemented for changing a shape of an antenna radiator by using a switching operation, so that it is effectively changed to a desired band and radiation pattern.
2. Description of the Related Art
Recently introduced portable terminals have various functions and designs. In addition, as the portable terminals are gradually becoming slimmer, lighter, and thinner, the functions of the portable terminals are more emphasized. To satisfy such costumers' demands, it is important to reduce the volume of the portable terminals while maintaining or improving the functions of the terminals.
More particularly, the aforementioned portable terminals can use antennas with the same antenna radiator at various bands, and thus the antenna radiator is changed or replaced to the minimum extent possible when there is a change in bands or radiation patterns. Therefore, there is an ongoing competition to decrease a size of the portable terminal and a Specific Absorption Rate (SAR) of electromagnetic waves of a terminal user.
As the antenna of the portable terminal uses a built-in antenna radiator, a Planar Inverted-F Antenna (PIFA) type has been implemented in recent years.
However, there is a problem in that the PIFA-type antenna has a fixed frequency property when a pattern, a feeding position, and a shorting point position are determined and in that the size of the antenna has to be increased in proportion to the number of supported bands.
In order to address this problem, a switching element capable of changing a position of an antenna ground may be placed, or the switching element may be placed on a path around an antenna signal input part so as to change an electrical length, which is used as a switching method at a frequency band of Global System for Mobile Communications (GSM) 850/900.
As the portable terminal becomes smaller and slimmer, the antenna occupies a very limited space in the terminal. However, global roaming and integration of communication services require implementation of a multi-band antenna. Since various resonance lengths should be implemented in the multi-band antenna, it is difficult to support all multiple bands required in a decreased antenna space, and performance deteriorates in some bands since an antenna gain is not sufficiently ensured. To address this problem, different antennas can be developed according to regions where portable terminals are used even if the portable terminals have the same design and hardware structure. However, this is not a proper method where customers want to use one terminal regardless of where they travel in the world. In addition, additional development costs are incurred due to antenna modification, and a delay in development schedule, a mechanical change for ensuring performance required in each region, approval costs, etc., are also problematic from the perspective of manufacturers.
As one method of addressing the aforementioned problems, a band control antenna can be used by utilizing an additional end portion connected to a switch so that it can be closed/opened with respect to a fixed end portion.
However, the design of the antenna may be limited when using this method since the position and pattern of the end portion connected to the switch are selected under the influence of the fixed end portion. Therefore, it may be difficult to design an antenna space in the complex structure due to various designs of the portable terminal.
In addition, antennas having the aforementioned structure can use this method in which a resonance frequency is changed through GSM 850 and GSM 900 band switching so that only a multi-band function can be processed by using the same antenna. Therefore, a change in the radiation pattern of the related art or an influence on the human body is not taken into account in this method.
Therefore, a need exists for a re-configurable built-in antenna of a portable terminal implemented to be able to exhibit a satisfactory radiation property even if a space for installing the same antenna radiator is used.